What's Making You Fat?

More to the Problem Than Genes

How’s this for a weighty statistic: Nearly two-thirds of Americans (65 percent) are now overweight, according to a new study that was published in the Journal of the American Medical Association. This means that despite the 33 billion dollars spent on diet products each year, the only thing getting lighter is our wallet.

Although some scientists say there are folks who are genetically inclined to be heavier than others, the magnitude of the obesity epidemic and the speed with which it exploded in recent years means there’s more to the problem than a fat gene.

“When things change that quickly, something in the environment is influencing the equation,” according to Donald Hensrud, M.D., associate professor of preventive medicine and nutrition at the Mayo Clinic in Rochester, Minnesota.

There’s no hard data to point the finger at any particular cause, though experts have bushels of theories: reduced physical activity, enormous portions, skyrocketing soda consumption, on-demand fast food, gulp-and-go dining and fat-free products loaded with sugar. Still, it all boils down to calories, calories, calories.

The solution is clearly to cut calories. But which calories to cut? Conventional wisdom says cut the fat. Wrong! Gobble all the fat you want, they say, it’s the carbs that have to go. Cut the fat? Cut the carbs? Whew! It’s enough to make your head whirl like a diet shake in a blender. Here’s the skinny on what’s making America fat and the bottom line on how to slim down.

Is Fat Making You Fat?

The Conundrum:

For decades, the dictum “You are what you eat” was commonly accepted. In other words, if you ate fat, you got fat. It made sense: Fat has nine calories per gram, compared to carbs and protein, which each have only four calories per gram. So logic held that by cutting back on fat you’d naturally lose weight.

But lately the idea has begun to circulate that a low-fat/high-carb diet could make you fat. How can this be? The theory is that reducing fat leads you to fill up on starchy carbs like white potatoes and refined white pasta, rice and bread — which are more quickly metabolized, causing blood sugar levels to swing.

Staunch carb opponents believe this leaves you hungrier, so you’re inclined to eat more. And because high blood sugar levels prompt the production of more insulin — a hormone that compels your body to store fat — you’re primed to sock away more fat. By the same token, eating less starch and more fat smooths out those blood sugar swings and slows digestion so you can go longer stretches without dashing to the refrigerator.

The Science:

Opponents of “fat makes you fat” circle the wagons around the idea that although we’ve lowered our fat intake, since we’re still gaining weight at an alarming rate, fat clearly isn’t the culprit. In fact, say some nutrition experts, we haven’t reduced our fat intake at all. We may have reduced the percentage of fat calories we eat, but because we’re consuming vastly more calories overall, we’re actually eating the same amount of fat we always have — maybe more.

Scores of studies, including 48 reviewed by the National Heart, Lung, and Blood Institute, demonstrate that when people cut back on fat, they lose weight, and when they cut fat and calories, they shed even more.

Need more proof? The nearly 3,000 people enrolled in the National Weight Control Registry who have lost 30-plus pounds — and, perhaps more important, kept the weight off for at least a year — did so largely by combining a low-fat diet with an hour of moderate physical activity each day, the amount currently recommended by the Institute of Medicine in Washington, D.C.

Data from the Continuing Survey of Food Intake by Individuals, a long-term study tracking the eating habits of more than 10,000 people, show that those eating a high-fat/low-carb diet had the highest body mass index (BMI, which is a gauge of whether you’re at a normal weight, overweight or obese based on your weight and height). Those on a low-fat/high-carb diet had the lowest BMIs.

Dr. Hensrud Agrees:

He points to Asian countries, like Japan and China, where fat comprises just 10 percent of the diet, the percentage of calories that come from carbs is high, and obesity rates are low.

And what of the idea that since fat is so satisfying, you’re apt to eat less? Well, it turns out that meal to meal, fat is not as satiating as, say, protein or high-fiber carb foods. But it will put some joie de vivre back into dieting.

Between the low-fat Dean Ornish, M.D., diet on one end of the spectrum and the high-fat menu plan that Robert Atkins, M.D., espouses, there’s room to maneuver in the middle with a moderate amount of fat, according to Walter Willett, M.D., Dr.P.H., chair of the nutrition department at the Harvard School of Public Health in Boston. The latest research bears this out.

An 18-month randomized study done at Brigham and Women’s Hospital in Boston showed that when overweight people on a low-calorie diet (women ate 1,200 calories and men 1,500) got 35 percent of their calories from fat, they enjoyed it more and lost an average of nine pounds. Those who got 20 percent of calories from fat actually gained six-and-a-half pounds!

“The people in the moderate-fat group told us they didn’t feel like they were dieting,” says study author Kathy McManus, R.D. “They could still enjoy their favorite foods as long as they controlled the amounts.”

The Bottom line:

A little extra fat may help you stick to your weight-loss plan. The Institute of Medicine suggests that 20 to 35 percent of your total calories can come from fat. But it’s very individual; you have to figure out what works for you.

Rather than reaching for saturated or trans fats — which raise cholesterol and increase your risk for heart disease — choose monounsaturated and polyunsaturated fats such as those found in olive and canola oils, nuts, flaxseeds, salmon, sardines and avocados. Just remember that even healthy fats pack a lot of calories.

Are Carbs Making You Fat?

The Conundrum:

Recently, simple carbohydrates (such as sugar and refined grain products) have been demonized as the root of all weight gain, blamed for stoking our hunger until we just can’t help but gorge. Advocates of this position swear that nixing carbs curbs hunger and forces the body to burn fat.

What’s with the flip-flop? Have carbs become the new fat?

The Science:

It comes back to calories. Americans are eating more of them, as well as too many sugary and/or refined carbs. So it makes sense that cutting back on carbs helps with weight loss simply because, again, you’re trimming calories.

Health experts, however, are quick to point out that carbs per se are not the villain. In fact, what’s often forgotten in the debate is that complex carbohydrates — fruits, vegetables, legumes and whole grains — are also carbs. These dietary good guys are essential to a successful weight-loss plan for many reasons including the fact that they’re high in fiber: Fiber fills you up before you have a chance to eat too many calories. It also helps your body absorb food more slowly, preventing a rapid rise in blood sugar.

“A healthy diet isn’t just low in fat,” says Dean Ornish, M.D., founder and president of the Preventive Medicine Research Institute in Sausalito, California. “It’s low in simple carbs and high in whole grains, fruits and vegetables, which are high in disease-fighting nutrients and low in disease-causing substances. To the degree that you reduce fat and simple carbs, you’ll lose weight and be healthier.”

It’s a view that — surprisingly — even those in the Dr. Atkins camp share. “You can succeed on a low-fat diet if you control your calories and choose foods such as fruits, vegetables and whole grains,” confirms Colette Heimowitz, director of education and research at the Atkins Health and Medical Information Services in New York City. “It’s when you add refined carbs to the mix that you run into trouble.”

The Bottom line:

Not all carbs are evil, but they’re not created equal, either. So you should dump the junk in favor of those that are highest in nutrients and fiber.

The Bottom Bottom Line: Regardless of the camp they’re in, weight-loss experts agree that if you want to lose weight, you need to cut calories — period. The key is finding a weight-loss plan that suits you.

Radically skewing your diet toward one food group or another means the possibility of missing out on certain nutrients. And you might regain the weight. “Your body begins to crave what you haven’t been eating,” according to Lee Kaplan, M.D., Ph.D., director of the MGH Weight Center at Massachusetts General Hospital in Boston. That’s why people can’t stick with diets strongly biased toward one group of nutrients or another for very long.

Finally, get some exercise. Hosts of studies show that combining working out with cutting calories helps keep the weight off.